Air pressure responsive oil burner control system



July 24, 1956 R. R. WITHERELL AIR PRESSURE RESPONSIVE OIL. BURNER CONTROL SYSTEM 3 Sheets-Sheet 1 Original Filed Oct. 28, 1950 IN V EN TOR.

Raamr R. wnutnsu. BY

ATTORNEY July 24, 1956 R. R. WITHERELL 2,755,848 AIR PRESSURE RESPONSIVE OIL BURNER CONTROL SYSTEM Original Filed Oct. 28, 1950 3 Shee ts-Sheet 2 m 1mg:

IN V EN TOR.

Roan? r R. N1 mean L AT TORNEY July 24, 1956 R. R. WITHERELL AIR PRESSURE RESPONSIVE OIL. BURNER CONTROL SYSTEM 3 Sheets-Sheet 3 Original Filed Oct. 28, 1950 INVEN TOR.

Rone'RT R. wlrnmcu.

AIR PRESSURE RESPONSIVE OIL BURNER CONTROL SYSTEM Robert R. Witherell, Bloomington, Ill., assignor, by mesne assignments, to Eureka Williams Corporation, a corporation of New York Original application October 28, 1950, Serial No. 192,669. Divided and this application February 26, 1952, Serial N0. 273,401

4 Claims. (Cl. 158-28) This invention relates to heating apparatus of the liquid fuel burning type and has particular reference to a control system for controlling operation of a liquid fuel burner. The liquid fuel burning system to which this application relates is of the low pressure air atomization type wherein a fraction of the air required to support combustion is compressed above atmospheric pressure and delivered to an air and oil mixing nozzle which atomizes the fuel into a spray of finely divided particles and discharges such spray into a stream of secondary air which flows past said nozzle. The control system of this invention precludes the flow of oil to the oil and air mixing nozzle except under normal operating conditions of the burner.

As now manufactured, liquid fuel burning systems of this type are relatively expensive. This invention contemplates a liquid fuel burning system of this type which is relatively simple in construction and hence may be manufactured and sold at a materially lower price than is now possible with known systems of this type.

A principal object of the invention, therefore, is to provide a new and improved control arrangement for a liquid fuel burner of the type referred to herein.

Another object of the invention is to provide a control arrangement for a liquid fuel burner which precludes the flow of oil to the oil and air mixing nozzle of the burner except under normal operating conditions of the burner.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are three sheets, which by way of illustration show a preferred embodiment of the invention and what I now consider to be the best mode in which I have contemplated applying the principles of my invention. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

Fig. 1 is a schematic illustration of a liquid fuel burning system embodying the invention;

Fig. 2 is a schematic wiring diagram of a control system for the fuel burning system illustrated in Fig. 1;

Fig. 3 is a vertical sectional view, with parts broken away, of the heating apparatus embodying the invention; and

Fig. 4 is a side elevational view, with parts broken away, of the apparatus illustrated in Fig. 3.

As shown in Figs. 3 and 4, the heating apparatus comprises a furnace having a combustion chamber 20 formed by the interior of a heat exchanger 22, an air and oil mixing nozzle 24 arranged to discharge a mixture of oil and air into said combustion chamber, pumping means indicated generally at 26 driven by a motor 28 operable for supplying oil and air to the nozzle 24 such nozzle being constructed so as to mix the oil and air supplied thereto and to atomize the fuel into a spray of finely divided particles and to discharge the same in the form of an oil fog into the combustion chamber, air circulating nited States Patent O 2,755,848 Patented July 24, 1956 ice charged so as to form a combustible mixture therewith,

a blower 32 arranged for circulating air to be heated over the heat exchange surface of the heat exchanger 22, the motor 28 being connected to the blower 32, to the air circulating means 30 and to the oil and air pumping means 26 so as to operate the same. In addition, the heating apparatus includes a control and ignition system as illustrated in Fig. 2, the ignition system including a pair of spaced electrodes 34 positioned near the discharge end of the nozzle 24 and operable for igniting the oil and air mixture supplied to the combustion chamber.

As illustrated in Fig. 1, the liquid fuel burning system comprises in general a reservoir or container 40 for containing a body of oil and air under pressure, means including an oil pump 42 and an air pump 44 in the form of an air injector operated by a jet of oil discharged from the pump 42. for accumulating within the reservoir 40 a mass of air under pressure above and in contact with a body of oil indicated at 46 in the bottom of the reservoir. The nozzle 24 is provided with one or more restricted oil passages 48 and one or more restricted air passages 50, the oil and air passages 48 and 50 converging so as to mix the oil and air supplied thereto and to atomize the oil which is discharged in a spray of finely divided particles from the discharge orifice 52 of the nozzle. The oil and air mixing nozzle is shown only schematically in this application. The construction of such nozzle may be as shown in Williams U. S. Letters Patent No. 1,934,755, issued November 14, 1933.

The nozzle 24 is arranged within the end of an air tube 54 which conducts a stream of secondary air from the air circulating means or fan 30 past the nozzle 24. The oil and air mixture discharged from the nozzle 24 is discharged into the stream of secondary air so as to form a combustible mixture and this mixture is burned in the combustion chamber 29. The nozzle 24 as illustrated is arranged within an air cone 56, one end of which is provided with a series of openings 58 whereby secondary air from the air tube 54 may flow into the air cone. The other end of the air cone 56 is frusto-conical and terminates in a relatively large opening 60, the frusto-conical end of the air cone 56 deflecting the air stream into the spray or mixture discharged from the nozzle 24. The air cone 56 is arranged within a second air cone 62 similar in construction to the air cone 56. The air cones 56 and 62 thus divide the secondary air stream into two annular parts which are successively directed into the oil and air mixture discharged from the nozzle 24 so as to intimately mix therewith and form a combustible mixture. The spaced electrodes 34, of which there are two, are adapted to create a spark across the gap therebetween at the beginning of each cycle of burner operation so as to ignite the combustible mixture which then burns within the combustion chamber 20.

Oil under pressure is supplied to the nozzle 24 by means of a tube or pipe 64 which forms part of a communication or connection between the nozzle 24 and the fuel and air pumping means 26 of which the reservoir 40 and the pumps 42 and 44 form a part.

Air under pressure is supplied to the nozzle 24 by a tube or pipe 66 which forms part of a connection or communication between the nozzle 24 and the reservoir 40. It should be noted that the communication 66 opens at one end 63 within the reservoir 40 below a baffle 70 and that such communication is open at all times. The communication 66 terminates at the other end in the air passageways 50 within the nozzle 24, and such passageways, due to the cross sectional area and arrangement thereof, do restrict the flow of air from the reservoir 40 through the communication 66. The oil and air passages 48 and 50 of thenozzle and the oil supply line 64 thereto and the the points in the nozzle 24 where the passages 48 and 50 converge. It is contemplated that with the system disclosed oil and air will be supplied to the nozzle at a pressure somewhere between 2 and pounds per square inch, although the invention is not limited to pressures within this range. -It has been found, however, by experience that this range of pressures is particularly suitable for use in oil burners of the type herein disclosed. it should be noted that the communication 66 and the air passages 50 in the nozzle are always open.

The oil pump 42 may be of the gear type and include a pair of gears 72 and 74 having their teeth arranged to intermesh as shown in Fig. l. 'The gear 72 is mounted on a drive shaft76 which is journalled in the gear pump housing 78 and which shaft extends through a running seal indicated generally at 80 to the outside of the reservoir 40. The shaft 76 extends through the casing of the fan'30 and is suitably coupled directly to the shaft of the motor 28. The rotor 82 of the fan 30 surrounds the shaft 76 and is connected thereto for rotation therewith so that when the pump 42 is driven, the fan 30 will effect the flow of the secondary air stream through the air tube 54 which at one end is connected to the fan as shown in Figs. 3 and 4.

The pipe or conduit 86 which opens at its lower end into the bodyof oil 46 in the reservoir 40 conducts oil to the inlet passage 84 of the pump. Part of the conduit 86 is formed by an oil injector 88 which functions during operation of the pump 42 todraw oil into the reservoir 40 from the source of supply, as will be explained more fully hereinafter.

- The outlet or discharge port 90 of the pump opens into a conduit 92 which is arranged to supply a jet of oil to the air injector 44. The air injector 44includes a conical jet 94 connected to the conduit 92 so as to be supplied with oil therefrom. The jet 94 is arranged to discharge a plurality of jets of oil into the throat 96 of a venturi'98. The jet 94 and venturi 98 are arranged in a chamber 100 which communicates by means of passage 102 with valve chamber 104. Valve chamber 104 includes a valve seat 106, and a ball valve 108 is adapted to seat on the seat 106 by gravity. An air supply conduit 110 communicates with the valve chamber 104 and with atmosphere exteriorly of the reservoir 40.

When the pump 42 is operating, the jets of oil discharged by the jet 94 into the throat 96 of the venturi 98 will impart velocity to the surrounding air and cause air flow through the conduit 110, the valve chamber 104, the passage 102 and the chamber 100 into the venturi 98. A conduit 112 communicates with the venturi 98 and is arranged to discharge the oil and air which flow through the injector 44 against the top wall of the reservoir 40. The horizontal baflle 70 arranged in spaced relation with the top Wall of the reservoir 40 aids in separation of the oil and air discharged from the venturi and prevents oil froth from flowing into the inlet end 68 of the air supply tube 66. When the injector 44 is not operating, the ball valve 108 seats on the seat 106 and thereby prevents the escape of air from the reservoir. The injector 44 is constructed and arranged so as to accumulate a mass of air under pressure within the reservoir 40 above and in contact with the body of oil 46 therein. The oil which passes through the injector-44 returns to the body 46 thereof in the bottom of the reservoir 40.

A pipe or conduit 114 is connected at one end thereof to the conduit 92 and at its other end to a shutofi valve and metering means indicated generally at 116 and which includes a solenoid actuated valve member 118 arranged to seat on a seat 120. The valve 118, 120 controls the-flow of oil from the pipe 114 into the metering means wvhich consists of a series of restricted orifices 122, 124 .and 126. The body 128 of the valve and metering means includes passages 130 and 132, chamber 134, and passage 136 formed by the orifice 126 and passage 138 formed by the orifice 124.

When the valve member 1 18 is unseated, oil from the pump 42 is free to fiowthrough the line 114, the passages 130 and 132, and through the orifice 122 into-the chamber 134. The orifice 122 is of such size as to permit a relatively large flow of fuel (that is, large in relation to the amountof fuel burned) into the chamber 134. From the chamber 134 part of the fuel flows through-the orifice 124 and the passage 138 into the oil supply line 64 to the n ozz le,'t he orifice 124 accurately metering the flow of-oil to the nozzle.

flheexcess oil: flows through the orifice 126 and the passage 136 and the conduit 140 back tozthe reservoir 40. The size of the orifice 124 is less than that of the orifice 126, which in turn is smaller than the orifice 122. Air entrained in the oilin the chamber 134 will separate out and return to the reservoir along with the excess oil through the orifice 126 and the passage 136. The orifices 122,124 and 126 are so proportioned with reference to the quantity of oil supplied from the pump-42 and the pressure at which it is supplied to the orifice 122 so as to accurately meter the oil at the desired rateto the nozzle 24 through the oil supply line 64.

The useo'fthe-three metering orifices 122, 124 and 126 as shown in Fig. 1 permits use of orifice diameters 1 substantially larger'thari the quantity of oil burned would requirewith a single orifice at the pressure available. The orifice122 substantially reduces the pressure of the oil so that-the pressure in the chamber 134 is only slightly in excess of the pressure in the reservoir, and this reduced pressure. in. the-chamber 134 is efiective to force oil through theorifice 124 to the nozzle 24. Because of this low pressure, the orifice diameter 124 which meters fuel to thenozzle may; be relatively large. It will be apparent that flow of oil to the nozzle may be varied by adjusting the diameter of the orifice 126 which returns fuel to the pressure reservoir.

The valve -member*118 is normally closed so that on the off cycle ofthe fuel burner there will be a positive shutoff in the oil linebetween the reservoir 40 and the nozzle 24. The valve 118, 120 is opened in response to a predetermined airpressure within the reservoir 40, as

-will hereinafter be explained, so that when the air pressure 118,-120will-close :-However the air pressure in the .reservoirl40 will be dissipated through the air line 66 ,whichwillpurge'the nozzle passages of oil at the end of each cycle of-operation.

in the reservoir 40 falls below such anamount the valve Upon the starting ofi-the cycle of operation, air will .flowthrough :the line 66 tothe nozzle 24 and discharge therefrom before the valve 118, 120 opens so that when .such valve 118, 120doesopen, air at the requisite pressure willbe available at the nozzle to efiect the mixing of air and oil in the nozzle and the atomization of the oil as previouslydescribed.

As will be explained hereinafter, secondary air will also be suppliedpastthe nozzle 24 by the fan 30 before the valve 118, 120 opens so that when such valve does open and oilflows to the nozzle 24, secondary air will be avail- -able in sufficient quantity and at suflicient pressure to form a combustible mixture with the oil spray discharged from the nozzle 24. At the end of each cycle of burner operation the secondary airflow will continue after the valve 1'18, 120 closes so as to support combustion as long as there is anyflow of oil from the nozzle and so as to scavenge the combustion chamber of any oil vapors.

An' oil supply .line leading from an oil storage tank is connected to afitting- 152 having a passage154 which communicates with the interior of the reservoir 40. The passage 154 opens into a valve chamber 156 of a valve body 158 of a float control valve indicated generally at 160. A valve seat 162 forms a discharge 7 "orifice from the chamber 1 56 and a seat foraball valve 164 which a'biasea toward the valve seat 162 by a spring 166. A conduit 168 communicates with the valve chamber 156 below the valve seat 162 and also with the throat 170 of the venturi 88. A pin 172 is slidably arranged in a bore of the valve body 158 and is engaged at one end by one end of a lever 174 pivoted at 176. A float 178 is fixed to the other end of the lever 174 and floats in the body of oil 46 in the bottom of the reservoir. The upper end of the pin 172 is engageable with the ball valve 164 so as to unseat the same as shown in Fig. 1, thereby establishing communication between the oil line 150 and the throat 170 of the venturi 88 through the conduit 168, the valve chamber 156, and the passage 154. As the level of the body of oil 46 in the reservoir rises, the float 178 will rise and permit the spring 166 to seat the ball valve member 164 on its seat 162, thereby breaking the communication between the throat of the venturi 88 and the oil supply line 150.

However, when the level of oil in the reservoir falls, the arm 174 will be actuated by the float 178 to move the pin 172 so as to unseat the ball valve memer 164 and thereby permit the suction in the throat of the venturi 88 to be applied to the oil in the line 158 so as to cause a flow of oil through the line 150 and the valve chamber 156 and the conduit 168 into the venturi 88 and thence through the conduit 86 and the gear pump 42.

As previously set forth, some of the oil discharged by the pump 42 will pass through the injector 44 and be returned to the body of oil in the bottom of the reservoir, while another portion of the oil will flow through the conduit 114 and through the metering means 116 to the nozzle 24. The float control valve 168 together with the venturi 88 thus forms a means for supplying oil to the reservoir 40 and for maintaining oil in the reservoir at a predetermined minimum level. The lower end of the pipe 86 which supplies oil to the pump 42 is arranged near the bottom of the reservoir 48 so that when the pump 42 operates, oil will be drawn through the pipe 86 and the venturi 88 into the pump 42, part of such oil coming from the body thereof in the bottom of the reservoir 4t) and the other part thereof being supplied through the line 158 when the valve 168 is open.

From the foregoing it will thus be evident that during operation of the gear pump 42 oil will be supplied through the line 150 to the reservoir 40 whenever the level of oil in the reservoir falls below a predetermined amount. From the foregoing it will also be evident that the gear pump 42 and the injector 44, together with the reservoir 40, form a pumping means for supplying oil and air under pressure to the nozzle 24 and that the metering means 116 forms a means for metering the supply of oil to the nozzle 24.

Fig. 2 shows a diagram of an oil burner control system which may be employed with the oil burner system herein disclosed. The room thermostat indicated generally at 380 and the primary control indicated generally at 382 are conventional and may be replaced by other suitable controls, the primary control 302 and thermostat 308 shown being ones now marketed by the Minneapolis Honeywell Company.

From one side of the current supply line indicated at 304 current is fed by conductor 386 and fuse 308 and through switch 310 to conductor 312 which is connected to one side 314 of a fan switch indicated at 316. Current is fed from conductor 312 by conductor 318 to one side 320 of a limit switch indicated at 322. The other side 324 of the limit switch is connected by conductor 326 to the primary coil 328 of the primary control transformer. The other side of the primary 328 is connected by conductors 330 and 332 and switch 310 to the other side 334 of the line when the switch 310 is closed.

The control circuit is shown in Fig. 2 as it would be during the off cycle of the burner. When the room thermostat 300 calls for heat, the movable contact 336 will move to engage stationary contact 338, and movable contact 340 will move to engage stationary contact 342,

thereby energizing the primary control by closing a circuit through the secondary 343 of the primary control transformer. When this occurs the relay coil 344 will be energized, thereby moving the line voltage side 346 of the relay armature so as to bridge contacts 348 and 350, which closes the circuit through the primary coil 352 of the ignition transformer, thereby energizing the electrodes 34 so as to produce a spark in the gap between the electrodes. One side of the primary 352 of the ignition transformer is connected by conductor 354 to conductor 332, while the other side of primary 352 is connected by conductor 356 to contact 350. Contact 348 is connected by conductor 358 to conductor 326.

The energization of relay coil 344 will also cause the low voltage side 360 of the relay armature to bridge the contacts 362, 364 and 366, thereby closing a circuit through the coil 368 of a second relay and energizing the coil so as to move the line voltage side 370 of the armature thereof to bridge contacts 372 and 374, which closes the circuit through the coil 376 of a relay 378. This causes the armature 380 of relay 378 to bridge contacts 382 and 384, thereby closing the circuit through the motor 26 which drives the pump 42, the fan 30 and the blower 32 as previously described.

The pump 42 and the injector 44 will thus begin to accumulate air under pressure in the reservoir 40, and when sufiicient pressure is developed in the reservoir 40 it will actuate diaphragm 386 to close the contacts of switch 388. This will close a circuit through the coil 390 of solenoid valve 118, 128 and thereby move valve member 118 away from seat 120 which will permit flow of oil from the reservoir to the nozzle as previously described. As the electrodes 34 are energized at this time, the combustible mixture of oil and air produced off the end of the nozzle 24, as previously described, will be ignited.

The switch 392 of the primary control is a stack switch and arranged to be closed when the stack temperature begins to rise, which follows combustion in the combustion chamber 20. Closing of the switch 392 will shunt the safety switch heater 394 out of the room thermostat circuit, thereby permitting thermal switches 396 and 398 to open in the order named so as to break the circuit through the coil 344 of the relay, thereby permitting the armature 346, 360 to move so as to open the circuit through the primary of the ignition transformer. The closing of thermal switch 392 will maintain the coil 368 of the second relay in a closed circuit through the room thermostat.

The foregoing describes a normal starting sequence of burner operation, and the burner will continue in operation until the room temperature rises enough for the movable contact 340 to separate from contact 342 or until the limit control contacts of switch 400 open.

The switches 316 and 322 are arranged in the plenum chamber or bonnet of the furnace so as to be responsive to the temperature of the air which has circulated over the heat exchanger. After a flame has been established and the circulating air has reached a suitable temperature, the contacts of the switch 316 will be closed, thereby closing a by-pass circuit through the motor 26. When the room thermostat is satisfied, the primary control will be deenergized which will interrupt the current through the coil 376 of relay 378 and the current through the coil 398 of the solenoid valve, thereby causing the valve 118, 120 to close and shut off the flow of fuel to the nozzle. The motor 26, however, will continue to operate through the by-pass circuit established by closing of the switch 316 until the circulated air drops in temperature suflicient to cause the switch contact 316 to open.

The switch 388 is in series with a switch 389, the switch 389 being normally closed and the switch 388 being normally open but closed by the diaphragm 386 in response to a predetermined pressure in the reservoir 40. The diaphragm 386 is spring loaded in order to determine the pressure at which it will close the switch 388.

, is not shown.

iter em e nl e nq z e ztshorlibs sm sls ss r i i n. a q m inq sa r ssi in t ss re .40, the increased displacement. f thediaphragm 386 will cause the normally closed contacts of the switch 389 to open and interruptfiow of oil to the nozzle. An eventual locking out of the operationof-theoil burner-will subsequently follow due to theaction of theprirnary controls.

If at the beginning of a cycle of operation theoil does not ignite, the contacts of switch 392 will remain open and the flow of current through the switch 4 00,will;after approximately ninety (90) seconds cause'the switch. 400 to open, which will shut down the burner until the manual reset (not shown) is-actuated.

The control system also provides for shutting down the burner in the event of flame failure and for re-cycling after a power failure in a conventional manner.

Referring now to Figs. 3 and 4, the inlet 410 of the blower 32 is connected to the return air system and the .blower 32 during operation thereof is adapted to circulate air over the-heat exchanger. 22 soias to absorb heat therefrom. Pivoted shutters, 412 arranged across the outlet 414 of they furnace..may be thermostatically controlled so that when the temperature of the, airwhich has circulated over the heat exchanger is below a .predetermined degree, the shutters 412, will close and prevent any circulation of air through the heating system until the temperature of the air in theupper .part of the furnace reaches a predetermined degree. The thermostat for effecting opening and closing of the shutters 412 The heat exchanger 22 is providedwith a pipe 416 which is adapted to be connected tothechimney for conducting the products of combustion-awayfrom the combustion chamber 20 providedinteriorly of the heat exchanger 22.

The switches 316, 322, 396,398, 392 and 400 are all thermostatically operated switches, as are the switches of the room thermostat 300.

.tion of said pumping means, a normally closed, electrically operated oil control valve in the oil discharge line from said pumping means, a thermostat and a primary control responsive thereto, a motor circuit including said motor adapted to be energized by said primary .control when said thermostat calls for heat, acircuitfor said oil control valve in parallel with said motor. circuit, a normally open switch and a normally closedswitch in series in said valve circuit, pressure responsive means for closing said normally open switch in response to-the ;discharge of primary air under pressure fromsaidpumping means thereby energizing said valve circuit for opening said valve when said motor circuit is closed and said pumping means is delivering primary air under pressure, said pressure responsive means being adapted to open said normally closed switch when the primary air pressure is above a predetermined pressure.

2. In a heating apparatus including oil and air pumping means and an electricmotor for causing operation of said pumping means; a control system for said apparatus com- .prising a normally closed solenoid valve in the oil discharge line from said pumping means, a motor circuit including said motor, means for energizing said motor circuit, a circuit including said solenoid valve in parallel with said motor circuit, a normally open switch in said solenoid. circuit, pressure responsive means for closing said switch in response to the discharge of air under pressure from said pumping means thereby energizing said solenoid circuit for opening said valve when said motor circuit is closed and said pumping means is delivering air under pressure, a normally closed switch in series with said normally open switch, said pressure responsive means being adapted. to open said normally closed switch to deenergize said solenoid circuit when the air delivered by said pumping means exceeds a predetermined pressure.

3. In a heating apparatus including oil andprimary air pumpingmeans and an electric motor for operating said pumping means, a normally closed,. electrically operated oil shutotf valve in the oil discharge line from said pumping means, an electrical circuit for said motor, an electrical circuit in parallel with said motor circuit and in which said electrically operated valve is connected, a normally open switehin said valve circuit, pressure responsive means for closing said switch in response to ,pressure developed in the air discharge line from said ,purnping means, closing of said switch energizing said valve circuit to open said valve when said motor circuit is energized, and a normally closed switch in series with said normally open switch and adapted to be opened by said pressure responsive means for deenergizing said valve circuit when the air pressure developed by said pumping means exceeds a predetermined amount.

4. Ina heating apparatus including oil and primary air supply means, an electric motor for causing operation of said supply means, a normally closed, electrically operated oil control valve in the oil discharge line from said supply means, a motor circuit including said motor, meansfor energizing said motor circuit, a circuit for said \oil control valve in parallel with said motor circuit, a normally open switch in said valve circuit, means for closing said switch in response to the discharge of primary air under pressure from said supply means thereby energizing said valve circuit for opening said valve when said .rnotor circuit is energized and said supply means delivering primary air under pressure, and means for deenergizing said valve circuit when theprimary, pressure exceeds a predetermined amount.

References Cited in the file of thispatent UNITED STATES PATENTS 1,102,482 De Vilbiss July 7, 1914 1,732,174 Sweatt Oct. 15, 1929 2,022,513 Macchi Nov. 26, 1935 2,197,746 Matthes Apr.. 16, 1940 2,384,836 Holthouse Sept- 18, 1945 2,432,314 Holthouse Dec. 9, 1947 2,512,919 Collins et al June 27, 1950 2,581,942 Collins et al Jan. 8, 1952 2,582,827 Gibson Jan. 15, 1952 

